The actual golden rule of being visible to search engines as well as accessibility is build a site and pages with "if no javascript, then print simple html version of page." I recall days web coders were writing for three different browser engines ... now some write for whatever new toy they've found with little thought to their client's intended visitors.
I went to visit specification.website but it failed to load on my old browser ... then again I block a lot of scraping PII APIS areas.
Edit - my bad, I realised that site was meant for agents and not humans with browsers.